Varenyam Achal

Strain improvement of Sporosarcina pasteurii for enhanced urease and calcite production

Phenotypic mutants of Sporosarcina pasteurii (previously known as Bacillus pasteurii) (MTCC 1761) were developed by UV irradiation to test their ability to enhance urease activity and calcite production. Among the mutants, Bp M-3 was found to be more efficient compared to other mutants and wild-type strain. It produced the highest urease activity and calcite production compared to other isolates. The production of extracellular polymeric substances and biofilm was also higher in this mutant than other isolates. Microbial sand plugging results showed the highest calcite precipitation by Bp M-3 mutant. Scanning electron micrography, energy-dispersive X-ray and X-ray diffraction analyses evidenced the direct involvement of bacteria in CaCO3 precipitation. This study suggests that calcite production by the mutant through biomineralization processes is highly effective and may provide a useful strategy as a sealing agent for filling the gaps or cracks and fissures in any construction structures.

Biomineralization based remediation of As(III) contaminated soil by Sporosarcina ginsengisoli

Arsenic is a highly toxic metalloid and has posed high risk to the environment. As(III) is highly mobile in soil and leached easily into groundwater. The current remediation techniques are not sufficient to immobilize this toxic element. In the present study, an As(III) tolerant bacterium Sporosarcina ginsengisoli CR5 was isolated from As contaminated soil of Urumqi, China. We investigated the role of microbial calcite precipitated by this bacterium to remediate soil contaminated with As(III). The bacterium was able to grow at high As(III) concentration of 50mM. In order to obtain arsenic distribution pattern, five stage soil sequential extraction was carried out. Arsenic mobility was found to significantly decrease in the exchangeable fraction of soil and subsequently the arsenic concentration was markedly increased in carbonated fraction after bioremediation. Microbially induced calcite precipitation (MICP) process in bioremediation was further confirmed by ATR-FTIR and XRD analyses. XRD spectra showed presence of various biomineralization products such as calcite, gwihabaite, aragonite and vaterite in bioremediated soil samples. The results from this study have implications that MICP based bioremediation by S. ginsengisoli is a viable, environmental friendly technology for remediation of the arsenic contaminated sites.

Effect of calcifying bacteria on permeation properties of concrete structures

Microbially enhanced calcite precipitation on concrete or mortar has become an important area of research regarding construction materials. This study examined the effect of calcite precipitation induced by Sporosarcina pasteurii (Bp M-3) on parameters affecting the durability of concrete or mortar. An inexpensive industrial waste, corn steep liquor (CSL), from starch industry was used as nutrient source for the growth of bacteria and calcite production, and the results obtained with CSL were compared with those of the standard commercial medium. Bacterial deposition of a layer of calcite on the surface of the specimens resulted in substantial decrease of water uptake, permeability, and chloride penetration compared with control specimens without bacteria. The results obtained with CSL medium were comparable to those obtained with standard medium, indicating the economization of the biocalcification process. The results suggest that calcifying bacteria play an important role in enhancing the durability of concrete structures.

Bioremediation of strontium (Sr) contaminated aquifer quartz sand based on carbonate precipitation induced by Sr resistant Halomonas sp.

Contamination of aquifers or sediments by radioactive strontium ((90)Sr) is a significant environmental problem. In the present study, microbially induced calcite precipitation (MICP) was evaluated for its potential to remediate strontium from aquifer quartz sand. A Sr resistant urease producing Halomonas sp. was characterized for its potential role in bioremediation. The bacterial strain removed 80% of Sr from soluble-exchangeable fraction of aquifer quartz sand. X-ray diffraction detected calcite, vaterite and aragonite along with calcite-strontianite (SrCO(3)) solid solution in bioremediated sample with indications that Sr was incorporated into the calcite. Scanning electron micrography coupled with energy-dispersive X-ray further confirmed MICP process in remediation. The study showed that MICP sequesters soluble strontium as biominerals and could play an important role in strontium bioremediation from both ecological and greener point of view.

Microbially-induced Carbonate Precipitation for Immobilization of Toxic Metals.

Rapid urbanization and industrialization resulting from growing populations contribute to environmental pollution by toxic metals and radionuclides which pose a threat to the environment and to human health. To combat this threat, it is important to develop remediation technologies based on natural processes that are sustainable. In recent years, a biomineralization process involving ureolytic microorganisms that leads to calcium carbonate precipitation has been found to be effective in immobilizing toxic metal pollutants. The advantage of using ureolytic organisms for bioremediating metal pollution in soil is their ability to immobilize toxic metals efficiently by precipitation or coprecipitation, independent of metal valence state and toxicity and the redox potential. This review summarizes current understanding of the ability of ureolytic microorganisms for carbonate biomineralization and applications of this process for toxic metal bioremediation. Microbial metal carbonate precipitation may also be relevant to detoxification of contaminated process streams and effluents as well as the production of novel carbonate biominerals and biorecovery of metals and radionuclides that form insoluble carbonates.

Corrosion Prevention of Reinforced Concrete with Microbial Calcite Precipitation

The corrosion of steel and reinforcing bar in concrete structures is one the most common reasons for civil infrastructure failures, especially for structures located in coastal and marine environments. Microbially induced calcite precipitation (MICP) on concrete or mortar is an important area of research to enhance the durability of construction materials. The effectiveness of MICP in reducing reinforcement corrosion is investigated in this article. Reinforced concrete (RC) specimens were treated with the bacterial strain Bacillus sp. CT-5, isolated from the cement sample, and subjected to accelerated corrosion. The results showed that bacterial-treated RC specimens reduced the corrosion rate four times more than the control specimens. A considerable reduction in mass loss and increase in pullout strength is observed with MICP-treated specimens. Corn steep liquor, an industrial pollutant, was used as a nutrient source to grow the bacterial cells for MICP in cementitious structures. This is a step toward the development of microbial concrete that provides a greener and more ecofriendly option.

Plant high tolerance to excess manganese related with root growth, manganese distribution and antioxidative enzyme activity in three grape cultivars

The cuttings of grape (Vitis vinifera Linn.) were exposed to Hoaglands solution containing five different manganese (Mn) concentrations to investigate Mn toxicity and the possible detoxifying responses. Three genotypes (i.e. cultivars Combiner, Jingshou and Shuijing) were used in present study. The results showed that grape species is highly tolerant to excess Mn. The plant growth is stimulated by as high as 15 or 30 mM Mn, and then depressed by higher Mn levels. The grape tolerance to excess Mn is related with plant capacity to keep constant or increased root growth as well as to keep high root activity. Also, the grape could employ some effective but intraspecific strategies to detoxify cellular Mn stress by excluding excess Mn out of leaf tissues or by enhancing antioxidative capacity. On the other hand, the present study showed that there existed different (or contrast) distribution pattern for excess Mn in grape. Majority of Mn was transferred and accumulated in the above-ground part in Combiner while Jingshou stored most Mn in root systems. For the first time our result showed the extreme tolerance and contrast performance at Mn translocation in an important fruit species with revealed genomic information.

Remediation of Cr(VI) from chromium slag by biocementation

Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM-EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.

Bio-grout based on microbially induced sand solidification by means of asparaginase activity

Bio-grout, a new ground improvement method, has been recently developed to improve the mechanical properties, decrease the permeability of porous materials, reinforce or repair cementitious materials and modify the properties of soil or sand. Bio-grout production depends on microbially induced calcite precipitation (MICP), which is driven mainly by an enzyme, urease. However, urease-based MICP process produces excessive ammonia, in addition to secondary pollution generated by urea that is used as substrate in it. In the present study, we reported asparaginase-based MICP process for sand bio-grout development using Bacillus megaterium, and results were also compared with urease-based bio-grouts. The asparaginase activity led to significantly less ammonia production compared to urease without compromising with desired properties of a novel grout. The UCS of bio-grout was obtained at 980 kPa, while the permeability was decreased substantially. The mineralogical composition of precipitated substance was identified as calcite using XRD and the crystal morphology was observed under SEM. The mass percentage of calcite in bio-grout was calculated by thermogravimetric analysis and XCT verified calcite precipitation in it. The results confirmed that biocalcification by means of bacterial asparaginase is a potential solution for geotechnical problems. The asparaginase-based MICP process could be of wider acceptance in future.

Proteomic Analysis of Mn-induced Resistance to Powdery Mildew in Grapevine

Previous studies documented that metal hyperaccumulation armours plants with direct defences against pathogens. In the present study, it was found that high leaf Mn concentrations (<2500 µg g(-1)) induced grapevine resistance to powdery mildew [Uncinula necator (Schw.) Burr]. Manganese delayed pathogen spreading after powdery mildew (PM) inoculation, but did not directly inhibit pathogen growth on a long-term basis. It was postulated that the grapevine resistance resulted from the induction of protective mechanisms in planta. To test this hypothesis, the proteome profile was analysed by Difference Gel Electrophoresis (DIGE) methods to identify proteins that are putatively involved in pathogen resistance. A high Mn concentration caused little oxidative pressure in grapevine, but oxidative stress was deeply enhanced by PM stress. Except for a few proteins that were related to oxidative pressure and proteins specially regulated by Mn or PM, most of the detected proteins exhibited similar changes under excess Mn stress and under PM stress, suggesting that similar signalling processes mediate the responses to the two stresses. As well as PM stress, high leaf Mn concentration significantly enhanced salicylic acid concentration and increased the expression of proteins involved in ethylene and jasmonic acid synthesis. The proteins related to pathogen resistance were also enhanced by excess Mn, including a PR-like protein, an NBS-LRR analogue, and a JOSL protein, and this was accompanied by the increased activity of phenylalanine ammonia lyase. It was concluded that high leaf Mn concentration triggered protective mechanisms against pathogens in grapevine.